Brains on Jazz Feel the Music

The pianist's languid solo entwines itself with the smoke and the muffled laughter from the bar. Like a shadow, the musician's fingers glide effortlessly across the keys, and he has no sheet music in front of him. Has he memorized the piece, or is he making it up as he goes along? It’s almost impossible to tell, but if you're a jazz musician and can imagine yourself playing the music, your brain’s emotional centers might help you answer this question, a new study suggests.

The ability to distinguish planned actions from spontaneous ones helps us judge whether a person is deliberately lying and might also help us value creativity. But it’s unclear how the brain makes these judgment calls, especially when it has little context to work with. To study how musicians judge spontaneity, psychologists Annerose Engel and Peter Keller of the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany, recorded six jazz pianists as each one played improvised jazz over a backing track. Then the researchers transcribed the pieces, handed out the sheet music, had the pianists practice until they could replicate their colleagues’ improv perfectly, and recorded their performances. A computer analysis of the recordings showed that each improvised piece was more erratic in its loudness and speed than its rehearsed counterpart.

So a machine could tell the difference between the improvised solos and the rehearsed reproductions. But could another musician? When a second set of 22 jazz musicians listened to all the improvised and rehearsed pieces in a random order, they could correctly guess which was which only about 55% of the time—only slightly better than chance—the researchers report in Frontiers in Psychology this month. However, the guessers who rated themselves in a questionnaire as more “empathetic” were better at picking out the improvisations. Similar correlations held true of those who had played with bands, as opposed to playing only as soloists.

All the listeners said that to make a judgment, they had to imagine themselves playing the piece in order to predict what would come next. They also paid particular attention to variations in loudness and speed. Brain scans backed this up: They showed that the amygdala—the center of the brain involved in emotion—became active as the listeners tried to put themselves in the player’s shoes. If a musician thought a piece of music was improvised, he activated the same brain networks that he would if they were improvising it themselves, including some motor centers that would let them physically play it.

Robert Zatorre, a neuroscientist at the Montreal Neurological Institute and Hospital at McGill University in Canada, says that the finding that the amygdala helps judge spontaneity is surprising and interesting but doesn’t definitively link spontaneity to emotion. “The coolest experiments are those that raise a lot of questions we didn’t know we needed to ask,” he says.

Engel hopes to follow up by studying the perception of spontaneity in other domains, such as dance or speech. However, she and Keller are both musicians who play several instruments, so jazz is close to their hearts and will likely remain a subject of their work. “It’s always a pleasure when you can combine work with a hobby,” she says.

Test Your Ear For Improv

Do you have the amygdala of a jazz musician? In each set of audio clips, one piece of music is improvised and the other is rehearsed. Click on the button next to the music sample you think is the improvised one of the pair.